Shelf Sea Biogeochemistry blog

Tuesday, 21 April 2015

Game of Filters: A Song of Filters and Water

The University of
Liverpool team (picture 1) is responsible for determining the composition and
relative concentrations of dissolved and particulate organic nutrients, namely
carbon, nitrogen and phosphorus. This is a key part of understanding both
nutrient cycling and the fate of carbon fixed by primary production in the shelf
system.

In real terms, this
equates to an awful lot of filtering during the SSB cruises. To achieve this we
travel down from Filterfell in the North to Southampton where we join the ship.
From then on, we employ all of the Seven Filtrations to collect a wide range of
samples. But first of all, we trot our little legs over to whichever device we
are using for sampling that day, be it Jon Snow Catcher, CTD or Ned SAPS, armed
with Tygon Lannister tubing and fill our bottles with as much seawater as we
can get our hands on. There is one exception however, when we are working
alongside the Fe Island team we aren’t trusted in the clean lab so they sample
their fancy CTD on our behalf and deliver the water to us.

During transects and at
designated stations we collect water samples from the CTD which we analyse for
dissolved organic nutrients, including dissolved organic phosphorus (DOP),
dissolved organic nitrogen (DON), dissolved organic carbon (DOC), amino acids
(AA) and coloured dissolved organic matter (CDOM). We define these nutrients as
those which pass through what is arguably the king of filters; King GFFrey with
a pore size of 0.7μm.

We collect a selfish
amount of water from the CTD for sampling particulate nutrients, including
particulate carbon, nitrogen, phosphorus, lipids, amino acids, stable nitrogen
isotopes and pigments. We define the particulate fraction as anything stuck to
King GFFrey after filtering a couple of litres of seawater (picture 2).We also collect particulate samples from the
now infamous Jon Snow Catcher.

A personal favourite for
sampling particulate nutrients is the honourable and reliable Ned SAPS. With
the help of Lord Commander Jon Short (picture 3), his Men of the NMF Watch, and
good old Ned SAPS we can filter hundreds of litres of seawater in situ,
separating out large particles from smaller ones which can give us useful
insight into the composition and variability of the different sized particles
in the water column.

Picture
3. [Lord Commander] Jon Short of the NMF [Watch] and good old [Ned] SAPS.
Photo: Chata Seguro.

After all the samples
have been filtered most are frozen in the freezer room which lies beyond the
great hangar, but the Cercei CDOM samples must be analysed on Hodor
Horiba…Horiba before they degrade. This is helps us calibrate the CDOM sensors
on Samuel ‘Tarly’ Ward’s sea gliders that roam the Celtic Sea.

While many are currently
playing in the Game of Filters, there is no denying that the North is a force
to be reckoned with as they rule over their Seven Filtration rigs across the
not-so-narrow Celtic Sea.

The bloom is coming! And
soon the seabed will be covered with marine snow…